1. Field of the Invention
The present invention relates to an engine cylinder head cover, and more specifically to a cylinder head cover for an internal combustion engine provided with blow-by gas flowing passages. Here, blow-by gas is a gas blowing into a crank case through spaces between the pistons and the cylinders during compression and explosion strokes and including non-combustion components such as HC, CO, etc., combustion components such as CO.sub.2, H.sub.2 O, N.sub.2, etc. and engine oil.
2. Description of the Prior Art
In general, the blow-by gas flowing passages for an internal combustion engine are formed to separate or remove engine oil (lubricant) from blow-by gas and further to return the blow-by gas into the intake system. In more detail, external air is introduced into the crank case from an upstream side of a throttle valve disposed in the intake passage through the cylinder head cover and scavenging holes formed in the cylinder head and the cylinder block, in order to scavenge the inner space of the crank case and the cylinder head cover, and further to return blow-by gas replaced with the external air through a blow-by gas outlet formed in the cylinder head cover to a downstream side of the throttle valve disposed in the intake passage. Further, since a fairly large amount of engine oil is included in the above-mentioned blow-by gas, in general some oil separating means are provided in the blow-by gas passage formed within the cylinder cover head, in order to prevent engine oil from being introduced into the intake passage.
An example of the above-mentioned oil separating means is disclosed in Japanese Published Unexamined (Kokai) Utility Model Appli. No. 63-37464, in which a roughly U-shaped breather chamber is formed in the cylinder head cover; blow-by gas introduced thereinto from one end of the breather chamber is turned along the U-shaped passage for oil separation; and further the turned blow-by gas is collided against a small amount of blow-by gas introduced from the other end of the breather chamber for additional oil separation. In this prior-art cylinder head cover, although a blow-by gas outlet is provided, since no external air inlet is formed, external air is directly introduced into the crank case of the internal combustion engine, and then the blow-by gas rising up through scavenging holes formed in the cylinder block and the cylinder-head is returned to the intake passage through the blow-by gas outlet.
In this prior-art structure, however, when the engine is running at high speed under heavy load, since pressure difference between the upstream side and the downstream of the throttle valve decreases, and further the amount of blow-by gas increases, there exists a problem in that blow-by gas flows through the external air passage in the reverse direction to the upstream side of the throttle valve in the intake passage, so that blown-by gas including engine oil is introduced into engine combustion chambers together with external intake air.
Therefore, where only the blow-by gas outlet and the oil separating means are provided in the cylinder head cover as in the prior-art case, without due consideration of the reversely flowing blown-by gas at high engine speed and under heavy load, it is inevitably necessary to provide an additional oil separating means at the external air inlet port on the crank case side, thus raising a problem in that the engine structure is rather complicated.